Pursuant to 35 USC xc2xa7119, this application claims the benefit of Japan Patent Application No. 2001-293063 filed Sep. 26, 2001.
The present invention relates to a method of manufacturing a commutator, an apparatus for manufacturing a commutator, and a commutator.
In general, a commutator has an approximately cylindrical insulator made of a resin and commutator pieces provided on the outer surface of the insulator. In a manufacturing method for a commutator, first, a cylinder is formed of a flat plate member and a molten resin is poured into the cavity of the cylinder. After the resin is cured, the cylinder is segmented at equiangular distances. The individual segments of the cylinder become commutator pieces and the cured resin becomes an insulator.
A plurality of projections (which correspond in number to the commutator pieces) extending in parallel to one another are formed, beforehand, at predetermined intervals on the surface of the flat plate member that is used to form the cylinder. Each projection has an extending portion which extends in a direction perpendicular to the lengthwise direction of the projection. When the cylinder is formed of the flat plate member, the individual extending portions are arranged on the inner surface of the cylinder. As each extending portion is engaged with the cured resin, each commutator piece obtained by segmenting the cylinder is prevented from being separated from the insulator.
In case of manufacturing a flat plate member for forming the aforementioned cylinder, as shown in FIG. 13, a plate member 52 which has projections 51, equal in number to commutator pieces, formed at predetermined intervals in such a way as to extend in parallel to one another is prepared first. The length of the plate member 52 in a direction perpendicular to the surface of the sheet of FIG. 13 is a predetermined integer multiple of the axial length of a single commutator in order to form a plurality of commutators (cylinders) from a single plate member 52. Next, a punch 54 is pressed against the plate member 52 placed on a mold 53 and a portion 52a of the plate member 52 is punched out of the plate member 52, as shown in FIG. 14. Thereafter, the punched-out portion 52a is segmented into plural segments each of which becomes a plate member for forming a commutator (cylinder).
The above-described manufacturing method provides a plate member for forming a plurality of commutators from a single plate member 52. This facilitates, for example, the handling of in the intermediate process (the stage before segmentation of the plate member 52) and management of parts, and can permit processing of a plate member for forming a plurality of commutators at a time. This can lead to reduction in manufacturing cost. Such a commutator manufacturing method is disclosed in, for example, Japanese Unexamined Patent Publication No. 2001-245456.
In the manufacturing method, the shape of the punch 54 is flat (see FIGS. 13 and 14), so that at the time of executing the punching step, the end portions of projections 51 on an end face 52b of the plate member 52 are smashed in the widthwise direction of the plate member 52, yielding a plurality of burrs 55 or die wears 56, as shown in FIG. 15. As the burrs 55 enter between the plate member 52 and the mold at the time of processing, punching marks are left on the surface of each commutator piece, resulting in improper contact with the brush or generation of noise. The die wears 56 make the thickness of the plate member 52 uneven. Those would bring about improper working in later processing (e.g., improper formation of the extending portions), resulting in the improper outer shape of the commutator or the separation of the commutator pieces from the insulator.
Accordingly, it is an object of the invention to provide a method of manufacturing a commutator, an apparatus for manufacturing a commutator, and a commutator, which can suppress the production of burrs or die wearing.
To achieve the object, according to one aspect of the invention, there is provided the following method of manufacturing a commutator. The method includes the steps of punching a commutator forming plate out of a plate member having a plurality of projections formed at predetermined intervals in such a way as to extend in parallel to one another, forming the commutator forming plate cylindrical and arranging the projections on an inner surface of the cylindrical commutator forming plate, filling an interior of the cylindrical commutator forming plate with a molten resin, segmenting the cylindrical commutator forming plate at predetermined angular distances after curing of the resin to thereby form commutator pieces, and positioning the plate member in a mold. The step of punching the commutator forming plate is carried out using a first punch having a plurality of recesses corresponding to the projections. Narrow portions are formed at those portions of each recess which correspond to both corner portions of the corresponding projection in such a way as to become narrower in a depth direction of that recess.
The invention further provides the following apparatus for manufacturing commutator. The apparatus punches a commutator forming plate of a predetermined length out of a plate member having a plurality of projections formed at predetermined intervals in such a way as to extend in parallel to one another by using a first punch. The first punch has a plurality of recesses corresponding to the projections. The commutator forming plate is formed cylindrical in such a way that the projections are arranged on an inner surface of the cylindrical commutator forming plate. The interior of the cylindrical commutator forming plate is filled with a molten resin. The cylindrical commutator forming plate is segmented at predetermined angular distances after curing of the resin to thereby form commutator pieces. The first punch has narrow portions each formed at those portions of each recess which correspond to both corner portions of the corresponding projection in such a way as to become narrower in a depth direction of that recess.
Furthermore, the invention provides the following method of manufacturing a commutator forming plate. The method comprises the steps of preparing a plate member having a plurality of projections formed at predetermined intervals in such a way as to extend in parallel to one another; and punching a commutator forming plate of a predetermined length out of the plate member using a first punch having a plurality of recesses corresponding to the projections and narrow portions each formed at those portions of each recess which correspond to both corner portions of the corresponding projection in such a way as to become narrower in a depth direction of that recess.
Moreover, the invention provides the following apparatus for manufacturing commutator forming plate. The apparatus punches a commutator forming plate out of a plate member having a plurality of projections formed at predetermined intervals in such a way as to extend in parallel to one another by using a first punch. The first punch has a plurality of recesses corresponding to the projections. Narrow portions are formed at those portions of each recess which correspond to both corner portions of the corresponding projection in such a way as to become narrower in a depth direction of that recess.
Further, the invention provides the following commutator forming plate. The commutator forming plate is used to form a commutator. The commutator forming plate has a plurality of projections formed at predetermined intervals in such a way as to extend in parallel to one another. Each projection has an extending portion extending in a direction perpendicular to a lengthwise direction of that projection. A plurality of commutator pieces are acquired by segmenting the commutator forming plate into a plurality of sections along the lengthwise direction of the projections. Each extending portion is secured to an approximately cylindrical insulator to constitute a commutator. The commutator forming plate has cut portions formed by punching the commutator forming plate by using a first punch having a plurality of recesses corresponding to the projections. The first punch has narrow portions each formed at those portions of each recess which correspond to both corner portions of the corresponding projection in such a way as to become narrower in a depth direction of that recess.
Furthermore, the invention provides the following commutator. The commutator comprises an approximately cylindrical insulator, and a plurality of commutator pieces to be secured to an outer surface of the insulator. The individual commutator pieces are acquired by segmenting a plate member having a plurality of projections extending in parallel to one another. Each projection has an extending portion extending in a direction perpendicular to a lengthwise direction of that projection. The commutator pieces have cut portions punched out by a first punch having a plurality of recesses corresponding to the projections. Narrow portions are each formed at those portions of each recess which correspond to both corner portions of each projection in such a way as to become narrower in a depth direction of that recess. The extending portion is engaged with the insulator in a radial direction of the commutator.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings that illustrate by way of example the principle of the invention.